1. Field of the Invention
The present invention relates to a continuously variable transmission. More particularly, the present invention relates to a continuously variable transmission including two pulley-type continuously variable transmission mechanisms and a planetary gear mechanism that combines two input components to output them as one output component.
2. Description of the Related Art
Hitherto, one such known type of continuously variable transmission includes two pulley-type continuously variable transmission mechanisms (variators) disposed in parallel between an input shaft and an output shaft. The two variators each include a belt or a chain and an input-shaft side pulley and an output-shaft side pulley. The pulleys clamp the corresponding belt or chain. Two output components output from the respective variators are input to a planetary gear mechanism, and are combined, so that they are output as one output component. (Refer to, for example, Japanese Unexamined Patent Application Publication Nos. 52-79172 and 63-9770.)
However, in each of the above-described related continuously variable transmission, pulley moving devices (for example, a hydraulic chamber, a hydraulic cylinder, or a driving motor) are provided at the back portions of four movable pulleys for controlling a speed-change ratio by changing the widths of the pulleys. Therefore, the input shaft and the output shaft become long, thereby increasing the size of the continuously variable transmission. Consequently, installation to a vehicle becomes difficult.
In addition, each of the above-described related continuously variable transmission is formed so that two output components output from the two variators are input to a ring gear and a sun gear of the planetary gear mechanism, respectively, to output them as one output component from a planetary carrier. Therefore, although there is difference between the speed of the sun gear and the speed of the ring gear, the directions of rotation are the same. Consequently, the planetary carrier rotates forwardly in accordance with the direction of rotation, but cannot rotate in the reverse direction or perform neutral rotation. Thus, a forward-backward movement switching device and a switching clutch are required.